1. Field of the Invention
The present invention relates to a gas collecting apparatus for collecting a trace quantity of gas components or volatile components in atmospheric air to continuously monitor the gas components or volatile components, a gas analyzing system using the gas collecting apparatus, and a gas analyzing method.
2. Description of the Related Art
The following two methods have been hitherto utilized as a method of analyzing gas components in atmospheric air. According to one method, an analysis operator collects samples in the field and carries them back to an analysis room to make analyses on the samples with various analysis methods. According to the other method, with respect to special components, an analysis apparatus comprising a sensor and a recording device is deployed in the field to monitor these special components. The sample collection work (sampling work) in the field is frequently performed by causing analysis components (samples) to be absorbed by absorption liquid or absorbent. When the absorption liquid is used, the analysis of the components is performed by using the absorption liquid itself. On the other hand, when the absorbent is used, the analysis of the components is performed by using extraction liquid (eluate) which has obtained by adding eluent to the absorbent to elute the components.
Liquid chromatography such as a high-speed liquid chromatography, ion chromatography or the like has merit in that many components in liquid can be analyzed with high sensitivity by using only one sample. Particularly, the ion chromatography used to analyze inorganic components can more easily analyze anion components for which an analysis operation becomes more cumbersome using other analysis methods, and this causes ion chromatography to be widely utilized. Even in the case of analysis of acidic gas components in the atmospheric air, the method of carrying the samples back to an analysis room and then analyzing absorption liquid or extraction liquid with the ion chromatography is mainly used as described above.
According to a widely used method based on use of absorption liquid, a predetermined amount of absorption liquid is fed into a bubbler or an impinger and the atmospheric air is sucked into the bubbler or the impinger and then bubbling or impinging is carried out to solve an analysis target component into absorption liquid. At present, an automatic monitor using this method has been developed, and the monitoring on the ground can be carried out.
Another easily automated method which has been developed incorporates a sample collection method using a gas permeable membrane (so-called diffusion scrubber method) as disclosed in "Analytical Chemistry", Vol. 61, No. 1 (January 1989), pp19-24, Japanese Patent Application Laid-open No. Hei-8-54380.
FIG. 1 is a diagram showing the construction of a diffusion scrubber body in a conventional gas analysis apparatus. As shown in FIG. 1, a diffusion scrubber body 101 has an inner pipe 102 of a gas permeable membrane tube and an outer pipe 103 into which the inner pipe 102 is inserted.
In the diffusion scrubber body 101, analysis components in a sample of atmospheric air are absorbed by absorption liquid while the sample atmospheric air is passed into the inner pipe 102 and the absorption liquid is passed through the gap between the inner pipe 102 and the outer pipe 103.
In a special case, the diffusion scrubber method can collect analysis target components such as hydrochloric acid, nitric acid, ammonia, etc. with a high collection rate of 90% or more, however, in general cases, the collection rate is not so high. In addition, fine particles in the sample atmospheric air are adsorbed onto the surface of the gas permeable membrane, resulting in variation of the collection rate overtime. Accordingly, this method is suitably applied to analysis which is limited to a component such as ammonia or the like for which the collection rate is high, and carried out in a clean room where the amount of fine particles is very low. However, this method is not necessarily suitable for a case where the sample atmospheric air is normal outside air or indoor air and a case where impurity components in the sample atmospheric air are required to be qualitatively grasped. This problem occurs because the sample atmospheric air and the absorption liquid are not brought into direct contact with each other.
As means of solving this problem, a wet denuder method has been developed, and it is disclosed in "Analytical Chemistry", Vol. 63, No. 13, July 1991. A conventional gas analysis apparatus using the wet denuder method will be described hereunder with reference to FIGS. 2 and 3.
FIG. 2 is a diagram showing the overall construction of a conventional gas analysis apparatus using the wet denuder method, and FIG. 3 is an enlarged cross-sectional view showing the main body of the denuder.
In the conventional gas analysis apparatus 201 using the wet denuder method, absorption liquid is passed from the upper side to the lower side along the inner wall of a denuder 202 serving as a gas collection apparatus as shown in FIG. 2, and also sample atmospheric air is passed from the lower side to the upper side in the denuder 202 by actuating a suction pump 203. The flow rate of the sample atmospheric air flow caused by the suction pump 203 is adjusted by a flow-rate controller 217.
In the denuder 202, a silica gel coat glass pipe 204 obtained by growing a silica gel film on the inner wall of a glass pipe (hereinafter referred to as "glass pipe 204") is provided, on the upper portion thereof, with an absorption liquid supply tube 205 for supplying absorption liquid into the glass pipe 204, and a sample atmospheric air exhaust pipe 206 for exhausting the sample atmospheric air from the glass pipe 204. Further, the glass pipe 204 is also provided, on the lower portion thereof, with an absorption liquid exhausting tube 207 for exhausting the absorption liquid from the glass pipe 204, and a sample atmospheric air supply pipe 208 for supplying the sample atmospheric air into the glass pipe 204.
The absorption liquid supplied from the absorption liquid supply tube 205 into the glass pipe 204 is passed through a filter 206'; and then downwardly flows along the inner wall of the glass pipe 204. On the other hand, the sample atmospheric air supplied from the sample atmospheric air supply tube 208 is passed through the glass pipe 204, and then exhausted from the sample atmospheric air exhaust pipe 206. At this time, the absorption liquid and the sample atmospheric air come into direct contact with each other, so that analysis components in the sample atmospheric air are absorbed into the absorption liquid. The absorption liquid which has absorbed the analysis components are exhausted from the absorption liquid exhaust pipe 207 to the outside of the glass pipe 204.
The absorption liquid exhausted from the absorption liquid exhaust tube 207 is fed to an ion chromatograph 210 by a liquid feeding pump 209 shown in FIG. 2. As shown in FIG. 2, the ion chromatograph 210 includes flow path switching valves 211a and 211b for switching a flow path for the absorption liquid, sample loops 212a, 212b for temporarily stocking the absorption liquid, a separation column 213 for separating analysis components from the absorption liquid to make analyses on the components, a suppressor 214 and a conductivity detector 215.
The flow path of the absorption liquid fed to the ion chromatograph 210 is switched by the flow path switching valve 211a to temporarily stock the absorption liquid in the sample loop 212a or the sample loop 212b. Thereafter, by switching to the flow path switching valve 211b, the absorption liquid which is stocked in the sample loop 212a or the sample loop 212b flows through the separation column 213, the suppressor 214 and the conductivity detector 215 in this order by the liquid feeding pump 216, whereby the analysis components are separated from the absorption liquid. The analysis components thus separated are analyzed and the concentration of the analysis components in the sample atmospheric air is calculated on the basis of the analysis result.
According to the conventional gas analysis apparatus 201 thus constructed, the collection rate of the analysis components is dependent on the contact area of the absorption liquid and the sample atmospheric air, and precision of concentration measurement of the analysis components is dependent on the reproducibility of the contact area of the absorption liquid and the sample atmospheric air on the surface of the inner wall of the glass pipe 204. Therefore, in the conventional analysis apparatus 201, a silica gel film is formed on the surface of the inner wall of the glass pipe 204 to enhance the wettability of the absorption liquid on the surface of the inner wall of the glass pipe 204, and also to make the absorption liquid uniform. In addition, the absorption liquid supplied from the absorption liquid supply tube 205 is passed through the filter 206', whereby the absorption liquid is dispersed onto the overall surface of the inner wall of the glass pipe 204.
However, the conventional gas analysis apparatus has the following disadvantage. That is, when it is used for a long period organic components in the atmospheric air are adsorbed onto the surface of the silica gel film of the silica gel coat glass pipe serving as the gas collection apparatus. As a result, the wettability of the surface of the inner wall of the glass pipe is reduced where the organic components are adsorbed. Therefore, the wettability of the absorption liquid on the surface of the inner wall of the glass pipe is non-uniform, the collection rate of the analysis components is varied over time, and the measurement precision of the concentration of the analysis components is reduced.
In order to prevent the time variation of the collection rate, etc., it is necessary to clean the inner wall of the silica gel coat glass pipe with detergent or alcohol, and thus maintenance and cleaning must be periodically performed. This causes a burden on a user of the gas analysis apparatus.